An open mike caught French Prime Minister Nicolas Sarkozy calling Israeli Prime Minister Benjamin Netanyahu a “liar” during a catty conversation with President Obama last week, according to an Israeli Web site.

Citing an online French report, Ynet News said that the leaders had retired to a private room after speaking to reporters at a G20 meeting last Thursday when the conversation turned to Netanyahu.

“I cannot stand him,” Sarkozy hissed to Obama.

“He’s a liar.”

Obama quickly chimed in with his own Bibi blast: “You’re fed up with him, but I have to deal with him every day.”

The oblivious pair had no idea that their microphones were on during the exchange and that the conversation streamed straight into the headsets of stunned reporters outside.

Ynet said that the French Web site Arret Aur Images reported that assembled media members were asked to sign an agreement to squelch details of the conversation, and opted to keep it quiet.

“There were discussions between journalists, and they agreed not to publish the comments due to the sensitivity of the issue,” the site quoted a media member as saying.

“By the time the media services at the Elysées realized it, it was still on for at least three minutes,” another reporter told the site.

But word of the diplomatic flub eventually leaked out before being picked up by French media yesterday.

Netanyahu’s relationship with both leaders has been frosty at times, but the embarrassing leak stunned observers.